Insulin Resistance as an Adaptation: Helpful or Not?
It was commonly believed that insulin resistance, a precursor to type II diabetes, developed as an adaptation to periods of starvation in our evolutionary history. This hypothesis was based on the premise that in times of starvation the body could preserve glucose levels, important for the brain and tissue healing. In times of plenty the body could readily store fat for future energy. This was known as the “Thrifty Gene Hypothesis”. Individuals who had this gene adaptation were more likely to survive lean times and later reproduce offspring. Current research has found this hypothesis to be inadequate. In times of starvation, death is often caused by infection, not loss of fat stores. Newer theories hypothesize that many genes influence the development of insulin resistance. There is no one gene that would give particular advantage for survival on its own. Experts agree that diet and lifestyle plays an even larger role.
Activation of the immune system and inflammation during infection is thought to be an adaptive response leading to insulin resistance. Nutrients are redirected from skeletal muscle to fight infection. In our modern world, chronic inflammation from unhealthy diet and lifestyle habits are contributing to the development of insulin resistance.
Insulin resistance occurs when the cells of the body do not respond normally to the hormone insulin. Insulin is secreted into the blood by the beta cells of the pancreas. The role of insulin is to regulate blood sugar levels by being the key that allows glucose into the cell. It is produced all of the time, even when we are sleeping. Insulin levels rise in response to a meal. Foods high in carbohydrates, including grains, potatoes, fruit, refined sugar, and processed foods cause the biggest surges. In order for the body to get fuel from ingested carbohydrates, they have to be broken down into individual sugar molecules called monosaccharides. Glucose, a monosaccharide, is absorbed into the body and transported into the cells. Inside the cell, glucose is used to produce energy.
There are several causative factors for insulin resistance. Obesity alone is a risk factor for developing insulin resistance. People who have gastric bypasses have an almost immediate reduction in insulin resistance due to weight loss. A diet high in refined carbohydrates causes frequent spikes in insulin production (hyperinsulinemia) and contributes to insulin resistance. Consuming excess calories, whether from fats or carbohydrates, leads to greater fat storage and obesity.
The amount of insulin that the body can produce is limited. Blood sugar levels creep up when insulin can no longer keep it in check. This leads to type II diabetes. For 1/3 to 1/2 of the American population, it is the overfed state that is the biggest risk factor for insulin resistance leading to type II diabetes. Fat storage affects cell signaling, leading to inflammation and the development of insulin resistance. Fats stored around the organs and especially in the liver, known as “non-alcoholic fatty liver disease” are especially dangerous. Fat stored under the skin, known as “subcutaneous fat”, does not increase the risk of developing type II diabetes. Development of insulin resistance is also triggered by stress and insufficient exercise. There are many negative physical reactions to insulin resistance. It is associated with weight gain, inflammation, reduction in good cholesterol, and decreased fertility.
Benefits of Insulin
As detrimental to health as insulin resistance sounds, there are some benefits to it, both evolutionarily and functionally. Insulin allows the body to divert resources to where they are needed. During starvation muscles are spared when insulin resistance is higher. Higher insulin levels have a positive effect on the brain and cognition. People with insulin resistance benefit from consistent blood sugar levels, even when fasting or exercising. From an evolutionary perspective, insulin resistance may have helped people survive starvation and injury.
The risk of developing insulin resistance and later type II diabetes is believed to be, at least in part, an inherited trait. At least as much risk is related to diet and lifestyle habits. Obesity has been shown to be a consistent risk factor for developing insulin resistance and type II diabetes. Excess food is stored as fat, once the short-term energy needs of the body are met. Diets both high in carbohydrate and high in fat contribute to fat storage. When fat is stored around the organs of the abdomen, especially the liver, it creates inflammation and abnormal cell signaling leading to insulin resistance. Chronic inflammation may be driving the widespread incidence of insulin resistance and type II diabetes.
Dr. Stacey Munro is a Naturopathic physician who specializes in prevention and treatment of chronic health conditions. Following Naturopathic philosophy, she looks for the root cause, rather than just treating symptoms. Dr. Munro prescribes dietary and lifestyle changes, nutritional supplements, herbs, and other natural therapies.
Nature’s Helper Medical Clinic 178 Mountain Road, Suffield, CT